This invention relates to an improved screw advancing pawl for a strip advance and release mechanism of an apparatus which sequentially advances and drives fasteners retained in a holding strip.
Autofeed screwdriver tools are known including U.S. Pat. No. 5,570,618 to Habermehl, issued Nov. 5, 1996 and U.S. Pat. No. 5,974,662 to Habermehl, issued Aug. 10, 1997 which have an advance mechanism utilizing a pawl with a single pawl arm to engage a screwstrip and advance the screwstrip.
The present inventor has appreciated that under some abnormal conditions, such as when the tool is not operated in a proper manner, disadvantages arise in that the known single pawl may not be moved into a position to engage any screws remaining in the strip and the strip may drop out of the tool.
The invention at least partially overcomes the disadvantages of the prior art by providing a blocking and/or advance pawl mechanism for an autofeed fastener driving tool with at least two pawl arms with at least one of the pawl arms maintained rearward of a next fastener to be driven from a strip holding fasteners spaced in a row. Preferably, the advance pawl mechanism provides for simultaneously manual deactivation of the at least two pawl arms to permit withdrawal of the screwstrip.
An object of the present invention is to provide an improved pawl for use in an autofeed screwdriving tool.
Another object is to provide a pawl for blocking withdrawal of a screwstrip from an autofeed fastener driving tool which has two spaced arms each of which are adapted to block withdrawal of a screwstrip.
Another object is to provide a pawl for advancing screwstrips in an autofeed fastening tool which has two spaced arms to engage two spaced screws in the screwstrip.
Accordingly, in one aspect, the present invention provides an apparatus for sequentially driving fasteners from a fastener strip comprising a plurality of fasteners secured in a row in a holding strip, the apparatus comprising:
a slide body having a lateral screwstrip receiving channelway and a guideway bore intersecting the channelway, the channelway configured to slidably receive the strip;
an elongate driver shaft having a shaft axis of rotation, said shaft including a fastener driving bit for engaging and driving fasteners in succession into a workpiece, said shaft being journalled and longitudinally slidably housed in said bore for reciprocal movement relative the slide body between an engaged position and a withdrawn position;
an advance mechanism mounted to said slide body for incrementally forwardly advancing the strip carrying the screws in the strip with the axis of each screw to pass in succession along a plane of advance within the channelway into the bore, said advance mechanism including a linkage member housed in said slide body and reciprocally movable between an advanced position and a retracted position as a function of cyclical reciprocal relative movement of the slide body and driver shaft,
a pawl pivotally mounted on the linkage member for pivoting between a first blocking position and a second passage position,
the pawl having a first arm with a first screw engaging surface and a second arm with a second screw engaging surface,
in the first blocking position, both the first and second engagement surfaces are positioned in the plane of advance such that the first engagement surface blocks any screw in the screwstrip immediately forward of the first engagement surface from movement relative the first engagement surface rearwardly pass the first engagement surface and the second engagement surface blocks any screw in the screwstrip immediately forward of the second engagement surface for movement relative the second engagement surface rearwardly past the second engagement surface,
in the second passage position, both the first and second engagement surfaces are positioned out of the plane of advance such that they do not block screws in the screwstrip forward of the first or second engagement surfaces from movement relative the first and second engagement surfaces rearwardly past the first or second engagement surfaces.
Further aspects of the invention will become apparent upon review of the following detailed description.